Most of us know that junk food is unhealthy. We know that poor nutrition is related to heart problems, high blood pressure, and a host of other health ailments. You might even know that studies show that eating junk food has been linked to increases in depression.
We’re more likely to have an appetite for junk food when we’re sleep deprived and brain scans may help explain why. Using functional magnetic resonance imaging (fMRI), researchers scanned the brains of 23 healthy young adults, first after a normal night’s sleep and then after a sleepless night. They found impaired activity in the sleep-deprived brain’s frontal lobe, which governs complex decision-making, but increased activity in deeper brain centers that respond to rewards.
When they were sleep-deprived, participants favored unhealthy snacks and junk food. “What we have discovered is that high-level brain regions required for complex judgments and decisions become blunted by a lack of sleep, while more primal brain structures that control motivation and desire are amplified,” said Matthew Walker, professor of psychology and neuroscience at the University of California, Berkeley. “High-calorie foods also became significantly more desirable when participants were sleep-deprived. This combination of altered brain activity and decision-making may help explain why people who sleep less also tend to be overweight or obese.”
Previous studies have linked poor sleep to greater appetites, particularly for sweet and salty foods, but the latest findings provide a specific brain mechanism explaining why food choices change for the worse following a sleepless night.
“These results shed light on how the brain becomes impaired by sleep deprivation, leading to the selection of more unhealthy foods and, ultimately, higher rates of obesity,” said doctoral student Stephanie Greer, the study’s lead author.
For this study, published in Nature Communications, researchers measured brain activity as participants viewed a series of 80 food images that ranged from high to low-calorie and healthy and unhealthy, and rated their desire for each of the items. As an incentive, they were given the food they most craved after the MRI scan.
Food choices presented in the experiment ranged from fruits and vegetables, such as strawberries, apples, and carrots, to high-calorie burgers, pizza, and doughnuts—the more popular choices following a sleepless night.
On a positive note, Walker said, the findings indicate that “getting enough sleep is one factor that can help promote weight control by priming the brain mechanisms governing appropriate food choices.”